1. Field of the Invention
The present invention relates to a magnetic memory which accesses stored data by the presence or absence of cylindrical magnetic bubble domains or so-called magnetic bubbles, and more particularly to such a magnetic memory having a plurality of minor loops, a write line and a read line.
2. Description of the Prior Art
In a magnetic bubble memory, information is stored by a "1" or "0" signal represented by the presence or absence of a cylindrical magnetic domain called a magnetic bubble which can be stably present in a magnetic thin film under a biasing magnetic field of 50-500 Oersteads perpendicular to a chip plane. The magnetic bubble representing the information is usually stored in a propagation track of a loop configuration.
A typical example thereof is described in detail in an article "68K Bit Capacity 16 .mu.m-Period Magnetic Bubble Memory Chip Design with 2 .mu.m Minimum Feature" IEEE Transaction on Magnetics, Vol. MAG-12, No. 6, pages 614-617.
In the above magnetic bubble memory, a plurality of minor loops each comprising a propagation track for propagating magnetic bubbles in response to a driving magnetic field rotating in a chip plane are arranged, and a write line having a function to write information in the minor loops is arranged at one end of the minor loops while a read line having a function to read out the information stored in the minor loops is arranged at the other end of the minor loops.
In such a memory chip arrangement, in order to increase a memory capacity, it is necessary to increase the number of bits in each of the minor loops. When the number of minor loops is increased, the number of bits in the write line and the read line increase accordingly.
On the other hand, since there is a limit in shortening a rotation cycle of the driving magnetic field which drives the bubble memory, an access time and a cycle time of the memory increase as the capacity of the memory chip increases and they are substantially proportional to a square root of the memory chip capacity.